Axial turbine wheel blades and nozzles typically have internal passages through which a fluid such as compressor discharge air can be circulated to cool the component. This allows hotter turbine inlet temperatures to be employed, increasing the efficiency of the turbine in which the components are installed.
For the same reason, considerable interest has been expressed in internally cooled wheels for radial engines.
However, components such as those axial turbine parts identified above are currently made by casting the metal around a ceramic core and then leaching the ceramic from the interior of the casting with caustic soda.
This approach is entirely unsuitable for radial turbine wheels because the blades of such wheels tend to be long and thin and to have a high degree of curvature. Consequently, a ceramic core cannot be positioned with sufficient accuracy to permit casting. Furthermore, in the case of cooled wheels, the core would have to contain holes or perforations into which metal could flow to form pins and partitions in the component; and these would weaken the core to an unacceptable extent. Consequently, internally cooled radial turbine wheels of optimum design have not heretofore been available.